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This review article presents an overview of recent work on electrochemical biosensors developed using microfabrication processes, particularly sensors used to achieve sensitive and specific detection of DNA sequences. Such devices are important as they lend themselves to miniaturisation, reproducible mass-manufacture, and integration with other previously existing technologies and production methods. The review describes the current state of these biosensors, novel methods used to produce them or enhance their sensing properties, and pathways to deployment of a complete point-ofcare biosensing system in a clinical setting.

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Antibiotic resistance is a growing concern in the treatment of infectious disease worldwide. Point-of-care (PoC) assays which rapidly identify antibiotic resistance in a sample will allow for immediate targeted therapy which improves patient outcomes and helps maintain the effectiveness of current antibiotic stockpiles. Electrochemical assays offer many benefits, but translation from a benchtop measurement system to low-cost portable electrodes can be challenging. Using electrochemical and physical techniques, this study examines how different electrode surfaces and bio-recognition elements, i.e. the self-assembled monolayer (SAM), affect the performance of a biosensor measuring the hybridisation of a probe for antibiotic resistance to a target gene sequence in solution. We evaluate several commercially available electrodes which could be suitable for PoC testing with different SAM layers and show that electrode selection also plays an important role in overall biosensor performance.

The manipulation of ribosomal RNA ͑rRNA͒ extracted from E. coli cells by dielectrophoresis ͑DEP͒ has been demonstrated over the range of 3 kHz-50 MHz using interdigitated microelectrodes. Quantitative measurement using total internal reflection fluorescence microscopy of the time dependent collection indicated a positive DEP response characterized by a plateau between 3 kHz and 1 MHz followed by a decrease in response at higher frequencies. Negative DEP was observed above 9 MHz. The positive DEP response below 1 MHz is described by the ClausiusMossotti model and corresponds to an induced dipole moment of 3300 D with a polarizability of 7.8ϫ 10 −32 F m 2 . The negative DEP response above 9 MHz indicates that the rRNA molecules exhibit a net moment of Ϫ250 D, to give an effective permittivity value of 78.5 0 , close to that of the aqueous suspending medium, and a relatively small surface conductance value of ϳ0.1 nS. This suggests that our rRNA samples have a fairly open structure accessible to the surrounding water molecules, with counterions strongly bound to the charged phosphate groups in the rRNA backbone. These results are the first demonstration of DEP for fast capture and release of rRNA units, opening new opportunities for rRNA-based biosensing devices.